1&#39;-Substituted-spiro[pyrrolidine-3,3&#39;-indoline]-2,2&#39;,5-triones

ABSTRACT

The invention provides a pharmaceutical composition comprising an aldose reductase inhibitory 1&#39;-substituted-spiro[pyrrolidine-3,3&#39;-indoline]-2,2&#39;,5-trione of the formula: ##STR1## wherein Ra is (2-7C)alkyl or (3-7C)alkenyl, naphthylmethyl or cinnamyl optionally bearing one or two halogeno nuclear substituents, or Ra is benzyl optionally bearing one or two substituents and benzene ring A optionally bears one or two substituents, trifluoromethyl and nitro; or a salt thereof with a base affording a pharmaceutically acceptable cation; or a non-toxic, biodegradable precursor thereof; together with a pharmaceutically acceptable diluent or carrier. The invention also provides novel compounds of formula I and processes for their manufacture. 
     The compositions are of application in the treatment or prophylaxis of the side effects of diabetes or galactosemia.

This invention relates to novel pharmaceutical compositions whichcontain as active ingredient a cyclic imide having the property ofinhibiting the enzyme aldose reductase in vivo. More particularly, thecyclic imide is a 1'-substitutedspiro[pyrrolidine-3,3'-indoline]-2,2',5-trione and the compositions arein general useful in the treatment or prophylaxis of those complicationsof protracted diabetes or galactosemia which are due at least in part tothe undesirable tissue accumulation of sorbitol or galactitol,respectively.

The enzyme aldose reductase is responsible in man and other warm-bloodedanimals for the catalytic conversion of aldoses, for example glucose andgalactose, to the corresponding alditols, for example sorbitol andgalactitol respectively. Alditols penetrate cell membranes poorly and,once formed, tend to be removed only by further metabolism. As aconsequence, alditols tend to accumulate within cells where they areformed, for example in the lens, peripheral nerve tissue and kidney,causing a rise in internal osmotic pressure which may in turn besufficient to destroy or impair the function of the cells themselves. Inaddition, raised alditol levels may result in abnormal levels of theirmetabolites which may themselves impair or damage cellular function.However, the enzyme aldose reductase has a relatively low substrateaffinity, that is, it is only effective in the presence of relativelylarge concentrations of aldose. Such large concentrations of aldose arepresent in the clinical conditions of diabetes (excessive glucose) andgalactosemia (excessive galactose). As a consequence, inhibitors of theenzyme aldose reductase are useful in the reduction or prevention of thedevelopment of those complications of protracted diabetes orgalactosemia which may be due in part to the accumulation of sorbitol orgalactitol respectively. Such complications are, for example, macularoedema, cataract, retinopathy, nephropathy or impaired neuralconduction.

It is known that certain spiro-linked hydantoins (spiro-linkedimidazolidine-2,5-diones) derived from various bicyclic ketones areinhibitors of the enzyme aldose reductase, for example the compounds ofthe general formula: ##STR2## wherein Z is oxygen, sulphur, sulphinyl,sulphonyl, methylene or a direct bond, and Y stands for various optionalsubstituents described by Sarges in U.S. Pat. Ser. No. 4,117,230. Wehave now discovered that certain spiro-linked succinimides (spiro-linkedpyrrolidine-2,5-diones) of formula I below and which are derived fromindoline-2,3-diones possess potent aldose reductase inhibitoryproperties, and this is the basis for our invention. This discovery isparticularly surprising in view of the various chemical differencesinvolved, for example the replacement of the imidazolidine imino moiety(which is adjacent to the spiro-carbon) by methylene, and theintroduction of an N-substituted iminocarbonyl (NRa.CO) group in theα-position of the saturated ring, which position has hitherto only beenoccupied by methylene.

Certain of the spiro-linked succinimides of formula I are known [H.Schaefer, Archiv der pharmazie (Weinheim), 1970, 303, 183-191;Chem.Abs., 1970, 73, 3739]but have not hitherto been known to possessaldose reductase inhibitory properties.

According to the invention there is provided a pharmaceuticalcomposition comprising as active ingredient a1'-substituted-spiro[pyrrolidine-3,3'-indoline]-2,2', 5-trione of theformula: ##STR3## wherein Ra is (2-7C)alkyl or(3-7C)alkenyl,naphthylmethyl or cinnamyl optionally bearing one or twohalogeno nuclear substituents, or Ra is benzyl optionally bearing one ortwo substituents independently selected from halogeno, (1-4C)alkyl,(1-4C)alkoxy, cyano, nitro and trifluoromethyl, located in the 2, 3, 4or 5 position; and benzene ring A optionally bears one or twosubstituents independently selected from halogeno, (1-4C)alkyl,trifluoromethyl and nitro; or a salt thereof with a base affording apharmaceutically acceptable cation; or a non-toxic, biodegradableprecursor thereof; together with a pharmaceutically acceptable diluentor carrier.

The compounds of formula I are derivatives ofspiro[pyrrolidine-3,3'-indoline]-2,2',5-trione which will be numberedthroughout this specification as follows: ##STR4## Throughout thisspecification the terms Ra, Rb et cetera are used to signify genericradicals and have no other significance.

The compounds of formula I all possess at least one asymmetric carbonatom, namely the spiro carbon atom at position 3 of the pyrrolidinering. The compounds of formula I therefore exist, and may be isolated,in one or more racemic and optically active forms. This inventionencompasses the compounds of formula I in racemic form or in anyoptically-active form which possesses aldose reductase inhibitoryproperties, it being well known in the art how to prepare opticallyactive forms by resolution of the racemic form, or by synthesis fromoptically-active starting materials, and how to determine the aldosereductase inhibitory properties by the standard tests describedhereinbelow.

The compositions of the invention may be in a form suitable for oraladministration, for example in the form of a tablet, capsule, granule,dispersible powder, syrup, elixir, emulsion, suspension or gel; forparenteral administration, for example in the form of a sterileinjectable aqueous suspension or solution, or oily solution orsuspension; for rectal administration, for example in the form of asuppository ; or for topical administration to the eye, for example inthe form of an ointment, gel or sterile solution buffered at anophthalmically acceptable pH, for example in the range pH 7.0-7.6.

The compositions may be manufactured by normal techniques of pharmacyusing procedures, carriers and diluents well known in the art. Ingeneral oral compositions are preferred, but the exact form ofcomposition and route of administration may vary depending on the hostand aldose reductase containing tissue under treatment. Tablets maycontain in addition to a compound of formula I or a salt thereof(hereinafter referred to as the active ingredient) one or more inertdiluents and compression aids, for example lactose, magnesium carbonateor calcium phosphate; granulating and disintegrating agents, for examplesodium or calcium carboxymethylcellulose, microcrystalline cellulose ormaize starch; binding agents, for example polyvinylpyrrolidone orgelatine; wetting agents, for example sodium lauryl sulphate orpolysorbate; and lubricating agents, for example magnesium stearate.Tablets may be uncoated or they may be coated by known techniques toincrease stability, to mask unpalatable taste, or to delay release ofthe active ingredient. They may in addition contain one or moresweetening, flavouring and colouring agents.

Capsules may be of hard gelatine and may contain the active ingredientalone, or in admixture with one or more solid non-toxic diluents oragents such as those mentioned above. Alternatively, capsules may be ofsoft gelatine wherein the active ingredient is mixed with an oilymedium.

Syrups and elixirs are formulated with sweetening agents, for examplesucrose or saccharin, and may also contain one or more conventionaldemulcents, flavouring and colouring agents.

Emulsions and suspensions may contain one or more conventionalsuspending agents, for example sodium carboxymethylcellulose oraluminium magnesium silicate, and dispersing and wetting agents, forexample, a polysorbate, together with one or more conventional diluents,for example water, ethanol, glycerol, propylene glycol, polyethyleneglycol, or an edible vegetable or mineral oil.

Gels may contain one or more conventional gelling agents, for exampleanimal and vegetable fats, waxes, cellulose derivatives, silicones orpolyethylene glycols.

Dispersible powders and granules which are suitable for theextemporaneous preparation of an aqueous suspension or solution maycontain one or more conventional dispersing, suspending or wettingagents, buffering agents, or preservatives.

Compositions intended for parenteral or topical administration to theeye may be sterilised by conventional procedures.

Solutions for topical administration to the eye, for example in thetreatment of diabetic cataracts, may contain one or more conventionalbuffers, for example boric acid, sodium or potassium carbonate,bicarbonate, acetate or borate; gelling or thickening agents, forexample dextran, glycerol, cellulose derivatives or polyethylene glycol;or other conventional excipients well known in the art for use in thepreparation of ophthalmic compositions. Similarly, ointments for topicaladministration to the eye may contain conventional excipients such assoft paraffin together with emulsifying and or thickening agents such assorbitan monostearate.

Suppositories for administration of the active ingredient per rectum maybe prepared by mixing the active ingredient with one or moreconventional non-irritant excipients which are solid at ordinarytemperatures but liquid at rectal temperature and which will thus meltin the body, releasing the active ingredient.

All the pharmaceutical compositions may be conveniently formulatedtogether with a conventional anti-oxidant, for example sodiummetabisulphite, and/or a preservative, for example methyl or propylp-hydroxybenzoate.

Dosage unit forms of a composition of the invention, for exampletablets, capsules or suppositories will in general contain 10-500 mg. ofactive ingredient, depending on the form involved.

Solutions and ointments for topical administration to the eye will ingeneral contain 0.02-2.0% by weight of active ingredient.

A particular value for Ra when it is (2-7C)-alkyl is, for example,ethyl, propyl, butyl, pentyl, hexyl or heptyl. A particular value for Rawhen it is (3-7C)alkenyl is, for example, allyl, 2-methylallyl or3-butanol.

A particular value for Ra when it is naphthylmethyl or cinnamyl bearingone or two halogeno nuclear substituents is, for example,5-chloro-1-naphthylmethyl, 6-chloro-2-naphthylmethyl, 4-chlorocinnamylor 3,4-dichlorocinnamyl.

Particular values for substituents which may be present on benzene ringA or nuclear substituents as part of Ra are, by way of example:

for halogeno; fluoro, chloro, bromo or iodo;

for (1-4C)alkyl; methyl or ethyl; and

for (1-4C)alkoxy; methoxy or ethoxy.

The term non-toxic, biodegradable precursor includes derivatives of thecompounds of formula I defined above in which the imino hydrogen atom inthe pyrrolidine ring is replaced by a biodegradable protecting groupknown in the art, which group is, not inherently toxic and which iscapable of removal in vivo (for example by enzymic hydrolysis) toliberate the compound of formula I in sufficient quantity to inhibit theenzyme aldose reductase and without giving rise to pharmacologicallyunacceptable by-products. Examples of suitable groups for inclusion inbiodegradable precursors of compounds of formula I includealkoxycarbonyl, aralkoxycarbonyl, alkoxyoxalyl and1-(alkoxycarbonyloxy)alkyl groups, such as ethoxycarbonyl,t-butyloxycarbonyl, benzyloxycarbonyl, ethoxyoxalyl, methoxyoxalyl andpivaloyloxymethyl groups. The biodegradable precursors are not ingeneral themselves inhibitors of the enzyme aldose reductase, but areactive in vivo by virtue of removal of the biodegradable protectingradical. It will be apparent therefore that by suitable choice ofbiodegradable protecting groups (for example based on their generallyknown rates of enzymic degradation) it is possible to producebiodegradable precursors of compounds of formula I whose bioabsorptionand distribution properties differ from those of the compounds offormula I.

Specific values for benzene ring A of particular interest are, forexample, when it is unsubstituted or bears a fluoro, chloro, bromo,methyl or trifluoromethyl substituent located in the 5'-, 6'-, or7'-position, and especially a 5'-fluoro, 5'-chloro, 5'-bromo, 6'-fluoro,6'-chloro, 6'-methyl, 7'-fluoro, 7'-chloro, 7'-methyl or7'-trifluoromethyl substituent.

Specific values for Ra of particular interest are, for example, when itis propyl, butyl, pentyl, hexyl or heptyl, 1-naphthylmethyl,2-naphthylmethyl, cinnamyl, halogenocinnamyl (especially4-chlorocinnamyl), dihalogenocinnamyl (especially 3,4-dichlorocinnamyl),benzyl, (1-4C)alkylbenzyl (especially 4-methylbenzyl), halogeno- or(trifluoromethyl)-benzyl [especially 4-chlorobenzyl, 4-bromobenzyl,(3-trifluroomethyl)-benzyl or (4-trifluoromethyl)benzyl],ordihalogenobenzyl (especially 2,4-dichlorobenzyl,4-chloro-2-fluorobenzyl, 4-bromo-2-fluorobenzyl, 2-fluoro-4-iodobenzyl,3,4-dichlorobenzyl, 3-bromo-4-chlorobenzyl or 4-bromo-3-chlorobenzyl).

In general, when Ra is alkyl or alkenyl it is preferred that benzenering A bears at least one substituent and preferably at least onehalogeno substituent.

Specific groups of novel compounds of formula I which are of specialinterest are mentioned hereinafter. However, of the known compoundsdescribed by Schaefer (see above), the compounds1'-(4-chlorobenzyl)-spiro [pyrrolidine-3,3'-indoline]-2,2', 5-trione and1'-(3,4-dimethoxybenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione,or salts thereof, are of particular interest as active ingredients ofcompositions according to the invention.

Particular salts of compounds of formula I with bases affording apharmaceutically acceptable cation are, for example, alkali metal oralkaline earth metal salts, such as sodium, potassium, calcium ormagnesium salts, aluminium or ammonium salts or salts with organic basessuch as triethanolamine.

The invention also provides a novel1'-substituted-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione of theformula: ##STR5## wherein Ra is (2-7C)alkyl or (3-7C)alkenyl,naphthylmethyl or cinnamyl optionally bearing one or two halogenonuclear substituents, or Ra is benzyl optionally bearing one or twosubstituents independently selected from halogeno, (1-4C)alkyl,(1-4C)alkoxy, cyano, nitro and trifluoromethyl, located in the 2, 3, 4or 5 position; and benzene ring A optionally bears one or twosubstituents independently selected from halogeno, (1-4C)alkyl,trifluoromethyl and nitro; or a salt thereof with a base affording apharmaceutically acceptable cation; or a nontoxic biodegradableprecursor thereof; but excluding those compounds of formula I wherein Rais benzyl, 4chlorobenzyl or 3,4-dimethoxybenzyl and benzene ring A isunsubstituted, and 1'-benzyl-5'-chloro-spiro[pyrrolidine-3,3'-indoline]2,2',5-trione.

Particular values for Ra and benzene ring A are defined hereinbefore.

Specific groups of novel compounds of the invention are comprised by thefollowing:

(i) Ra has any of the meanings defined above; and benzene ring A issubstituted as defined above apart from by a 5-chloro substituent;

(ii) Ra is (2-7C)alkyl especially propyl, butyl, pentyl or hexyl or(3-7C)alkenyl especially allyl or 3-butenyl, naphthylmethyl or cinnamyloptionally bearing one or two halogeno nuclear substituents, or a benzylradical bearing one or two substituents as defined above; and benzenering A bears a 5-chloro substituent;

(iii) Ra has any of the meanings defined above apart from 4-chlorobenzylor 3,4-dimethoxybenzyl; and benzene ring A is unsubstituted;

(iv) Ra is (2-7C)alkyl or (3-7C)alkenyl; and benzene ring A has any ofthe meanings defined above;

(v) Ra is naphthylmethyl or cinnamyl optionally bearing one or twohalogeno substituents; and benzene ring A has any of the meaningsdefined above; or

(vi) Ra has any of the meanings defined above; and benzene ring A bearsa 5'-fluoro, 5'-bromo, 6'-halogeno (especially 6'-fluoro or 6'-chloro),6'-(1-4C)alkyl (especially 6'-methyl) 7'-halogeno (especially 7'-fluoroor 7'-chloro), 7'-(1-4C)alkyl (especially 7'-methyl), or7'-trifluoromethyl substituent;

together with in each group the salts thereof with bases affording apharmaceutically acceptable cation, and the non-toxic biodegradableprecursors thereof.

A preferred group of novel compounds of the invention comprises thosecompounds of formula I wherein Ra is benzyl as defined above bearing atleast one halogeno or trifluoromethyl substituent, and benzene ring Aoptionally bears one or two substituents as defined above located at the5', 6' or 7' position; together with the salts thereof, and thenon-toxic biodegradable precursors thereof; but excluding1'-(4-chlorobenzyl)-spiro[pyrrolidine-3;3'-indoline]-2,2',5-trione.

A second preferred group comprises those compounds of formula I whereinRa is benzyl bearing two independently selected halogeno substituentslocated at fluoro, 4-bromo-2-fluoro, 2-fluoro-4-iodo,2,4-dichloro-3,4-dichloro, 4-bromo-3-chloro and 3-bromo-4-chlorosubstituents), or Ra is benzyl bearing bromo or trifluoromethyl locatedat positions 3 or 4; and benzene ring A has any of the meanings definedimmediately above in the first preferred group; together with the saltsthereof, and the non-toxic biodegradable precursors thereof.

Specific novel compounds of formula I are provided in the accompanyingExamples. However, compounds of particular interest are, for example:

    ______________________________________                                        Ra                Benzene ring A substituent                                  ______________________________________                                        3,4-dichlorobenzyl                                                                              unsubstituted                                               2-fluoro-4-iodobenzyl                                                                           unsubstituted                                               4-bromo-2-fluorobenzyl                                                                          unsubstituted                                               4-bromo-2-fluorobenzyl                                                                          5'-chloro                                                   3,4-dichlorobenzyl                                                                              5'-chloro                                                   3,4-dichlorobenzyl                                                                              5'-fluoro                                                   3,4-dichlorobenzyl                                                                              7'-fluoro                                                   4-bromo-2-fluorobenzyl                                                                          7'-fluoro                                                   4-bromo-2-fluorobenzyl                                                                          7'-methyl                                                   2-fluoro-4-iodobenzyl                                                                           7'-fluoro                                                   ______________________________________                                    

together with the salts thereof, and non-toxic, biodegradable precursorsthereof.

A preferred non-toxic, biodegradable precursor is, for example,pivaloyloxymethyl.

The novel compounds of formula I may be obtained by any process known inthe art for the manufacture of structurally analogous compounds. Suchprocesses are provided as a further feature of the invention and areillustrated by the following procedures in which, unless otherwisestated, Ra and benzene ring A have any of the above mentioned values andare subject to the aforementioned disclaimers:

(a) Decarboxylating an acid of the formula: ##STR6## under the influenceof heat.

The decarboxylation may be carried out at a temperature in the range,for example, 60°-200° C. and a suitable solvent or diluent, for exampleacetic acid diethanolamine or quinoline (optionally together with copperpowder) may conveniently be present.

The starting materials of formula II are conveniently generated in situby hydrolysis of the corresponding derivative of the formula: ##STR7##wherein Rb is alkoxycarbonyl (such as methoxycarbonyl, ethoxycarbonyl ort-butoxycarbonyl), aralkoxycarbonyl (such as benzyloxycarbonyl), cyanoor carbamoyl. The hydrolysis may be carried out using conventional acidor base catalysed conditions, for example as illustrated in theaccompanying Examples, and at a temperature in the range, for example,40°-100° C. When base catalysis is used the acid of formula II must begenerated from the salt first obtained, by acidification with a mineralacid such as hydrochloric acid. When acid catalysis is used, the acid offormula II may undergo spontaneous decarboxylation to generate thecompound of formula I.

When Rb is an (α,α-dibranched)alkoxycarbonyl group, such ast-butoxycarbonyl, the acid of formula II may be generated by thermolysisat a temperature in the range, for example, 120°-180° C., preferably inthe absence of solvent or diluent and under reduced pressure. Underthese conditions the acid of formula II undergoes decarboxylation to thecompound of formula I.

When Rb is an aralkoxycarbonyl group, such as benzyloxycarbonyl, theacid of formula II may also be formed by conventional hydrogenolysis,for example using hydrogen at atmospheric pressure in a solvent, such asethanol or aqueous ethanol, using a palladium based catalyst.

Particularly convenient conditions for the in situ formation andsubsequent decarboxylation of an acid of formula II are provided byheating a derivative of formula III defined above in a (2-6C)alkanoicacid; such as acetic or propionic acid, in the presence of an inorganicacid, such as hydrogen chloride or hydrogen bromide, and at atemperature in the range for example, 100°-150° C. This process isincluded on a further feature of the invention.

The starting materials of formula III may be obtained by cyclisation ofa bifunctional derivative of the formula: ##STR8## wherein one of X, Yand Z is cyano or carbamoyl and the other two are independently selectedfrom cyano, carbamoyl, alkoxycarbonyl (such as methoxycarbonyl orethoxycarbonyl) and aralkoxycarbonyl (such as benzyloxycarbonyl). Apreferred value for X and Y is, for example, cyano and for Z is, forexample, methoxycarbonyl or ethoxycarbonyl.

This process is normally performed in the presence of an acid or basecatalyst, preferably in the presence of an inorganic acid catalyst suchas a hydrogen halide, sulphuric acid or polyphosphoric acid. The processis conveniently performed in a suitable solvent or diluent, for examplea (1-6C)-alkanol (such as methanol or ethanol) or a (2-6C)-alkanoic acid(such as acetic or propionic acid) and is normally carried out at atemperature in the range, for example 20° to 120° C. If somewhat highertemperatures are employed, it is possible to carry out the conversionto, and decarboxylation of, the acid of formula II in situ, for exampleby using hydrogen bromide in acetic acid at the boiling point of thereaction mixture.

The starting materials of formula IV may be obtained by conventionalprocedures of organic chemistry well known in the art. Thus, thosecompounds of formula IV wherein X is cyano may be obtained by additionof cyanide to an unsaturated compound of the formula: ##STR9## or ageometric isomer thereof, wherein Y and Z have the meanings definedabove, for example by reacting a compound of formula V with potassiumcyanide in methanol at a temperature in the general range 10° to 50° C.

The starting materials of formula V are themselves obtained from thecorresponding 1-substituted-indoline-2,3-diones of the formula:##STR10## by condensation with a compound of the formula Y.CH₂.Z,wherein Y and Z have the meanings defined above, preferably in thepresence of a base catalyst such as piperidine or morpholine, in asuitable solvent such as methanol or ethanol, and at a temperature inthe general range 10° to 100° C.

The compounds of formula Y.CH₂.Z and VI are in general well known in theart or may be obtained by conventional procedures, such as thoseillustrated in the accompanying Examples.

(b) Deprotecting a compound of the formula: ##STR11## wherein Rc is aprotecting group, for example formyl, (2-6C)alkanoyl, benzoyl,[(1-6C)alkoxy]carbonyl, benzyloxycarbonyl, benzylhydryl,triphenylmethyl(trityl) or tri-[(1-4C)alkyl]silyl, in particular formyl,acetyl, benzoyl, methoxycarbonyl, t-butoxycarbonyl, benzyloxycarbonyl,benzylhydryl, triphenylmethyl or trimethylsilyl.

It will be appreciated that, depending on the nature of the group Rc,different deprotection methods are involved. Thus, when Rc isbenzylhydryl, trityl or benzyloxycarbonyl, reductive deprotection may beemployed, for example using hydrogenation at or near atmosphericpressure in the presence of a suitable catalyst, such as palladium on aninert support, at a temperature in the range, for example 10° to 40° C.Also, when Rc is an acyl group, conventional acid or base catalysedhydrolysis may be used to carry out the deprotection, for example byreaction with a hydrogen halide in aqueous ethanol or acetic acid, orwith aqueous ethanolic sodium hydroxide or potassium hydroxide, at atemperature in the range 20° to 60° C. Further, when Rc is at-butoxycarbonyl or trimethylsilyl radical, the deprotection may becarried out at a temperature in the range, for example, 10° to 40° C.using a strong acid such as hydrochloric or trifluoroacetic acid,optionally in the presence of an inert diluent or solvent.

The starting materials of formula VII may be obtained, for example, byreacting a compound of the formula: ##STR12## with a halogeno compoundof the formula Ra.Hal wherein Hal is halogeno, especially chloro, bromoor iodo, in the presence of a base.

A suitable base is, for example, sodium or potassium hydride orcarbonate and a convenient solvent or diluent which may be used is, forexample, N,N-dimethylformamide or dimethyl sulphoxide. In general, thecompound of formula VIII will be reacted with the base before theaddition of the compound of the formula Ra.Hal. and the reaction will becarried out at a temperature in the range, for example 10° to 60° C.

The starting materials of formula VIII may be obtained by alkylation ofa salt of the formula: ##STR13## wherein M is an alkali metal cation,such as lithium, sodium or potassium, formed in situ by addition of onemolecular equivalent of a suitable base, such as butyl lithium, sodiumhydride or potassium hydride, to a solution of the compound of formulaIX (M═H) in a suitable polar solvent such as N,N-dimethylformamide,dimethyl sulphoxide, tetrahydrofuran, hexamethylphosphoramide orN-methyl-2-pyrrolidone, diluted if necessary with an inert diluent. Thealkylating agent will generally be a compound of the formula Rc.Hal asdefined above and the salt of formula IX will ordinarily be addeddropwise in solution to a solution of the alkylating agent in thereaction solvent, generally at a temperature in the range, for example-10° to 50° C., in order to minimise the possibility of alkylation atthe indoline nitrogen atom.

The starting materials of formula IX (M═H) may be obtained by ananalogous procedure to that in process (a) hereinabove but starting fromthe appropriate 1-unsubstituted indoline-2,3-dione (isatin) derivative.

(c) Alkylating a salt of the formula: ##STR14## wherein M is an alkalimetal cation as defined above, by reaction with an alkylating agent ofthe formula Ra.Q, wherein Q is a suitable leaving group such as halogeno(especially chloro, bromo or iodo, (1-6C)-alkylsulphonyloxy (especiallymethylsulphonyloxy) or arylsulphonyloxy (especially4-methylphenylsulphonyloxy).

The salt is preferably formed in situ by reaction of a compound offormula X (M═H) with at least two molecular equivalents of base, forexample an alkali metal hydride or hydroxide such as sodium or potassiumhydride, or sodium or potassium hydroxide. The process is preferablycarried out in a suitable polar solvent, for example a (1-4C)alkanol(such as methanol or ethanol), N,N-dimethylformamide or dimethylsulphoxide, optionally together with a suitable inert diluent, and at atemperature in the range, for example, 10° to 100° C. It is generallypreferred to use only a slight excess of the alkylating agent and to addit dropwise to the reaction mixture in order to minimise the possibilityof dialkylation occurring. The starting material of formula X (M═H) inthe above process can be obtained by an analogous procedure to process(a) starting from the appropriate 1-unsubstituted-indoline-2,3-dione(isatin)derivative.

(d) For a compound of formula I wherein benzene ring A bears a nitrosubstituent and/or Ra is benzyl bearing a nitro substituent, nitratingthe corresponding compound of formula I in which benzene ring A isunsubstituted or monosubstituted and/or Ra is unsubstituted benzyl ormonosubstituted benzyl.

The nitration may be carried out under conventional procedures, forexample in the presence of sulphuric acid, using nitric acid at atemperature in the range, for example, 0° to 30° C., or using fumingnitric acid at a temperature in the range, for example -20° to 10° C.

(e) For a compound of formula I wherein benzene ring A bears a chloro orbromo substituent, chlorinating or brominating the correspondingcompound of formula I wherein benzene ring A is unsubstituted ormonosubstituted.

The chlorination or bromination may be carried out using conventionalprocedures, for example using elemental chlorine or bromine, optionallyin the presence of a Friedel-Craft's catalyst, such as ferric chloride,ferric bromide or iron powder, at a temperature in the range, forexample 10° to 100° C. and in a suitable solvent or diluent, for examplechloroform, nitrobenzene or acetic acid.

Alternatively, the chlorination or bromination may be carried out usingsulphuryl chloride or bromide, optionally in the presence of iodine ascatalyst at a temperature in the range, for example 10° to 100° C., andin a suitable solvent or diluent, for example acetic acid or chloroform.

Processes (d) and (e) are particularly suitable for the production ofthose compounds of formula I in which benzene ring A bears a5-substituent using a compound in which benzene ring A is unsubstitutedas starting material.

The non-toxic, biodegradable precursors of the compounds of formula Imay be obtained by known acylation or alkylation procedures already usedfor the introduction of the necessary biodegradable protecting radicals.Examples of suitable acylating or alkylating reagents for incorporatinga range of such protecting radicals are, for example, alkoxycarbonyl,aralkoxycarbonyl, alkoxyoxalyl and 1-(alkoxycarbonyloxy)alkyl halides,such as ethoxycarbonyl, t-butyloxycarbonyl, benzyloxycarbonyl,ethoxyoxalyl, methoxyoxalyl and pivaloyloxymethyl chloride.

The reaction may be performed under conventional N-acylation/alkylationconditions, for example in the presence of a base such as potassiumcarbonate or using the lithium, sodium or potassium salt of the compoundof formula I, and in a suitable solvent or diluent, for example1,2-dimethoxyethane, di-n-butyl ether or diethyl ether, at a temperaturein the range, for example 10°-80° C.

The intermediates of formula III are novel and in many cases (forexample when Rb═CN and Ra is halogenobenzyl) possess aldose reductaseinhibitory properties in their own right. These novel intermediates offormula III and processes for their production as defined hereinaboveare therefore provided as a further feature of the invention. The novelintermediates of formula V and processes for their production as definedhereinbefore are also provided as a further feature of the invention.

Whereafter, when a pharmaceutically acceptable salt is required, acompound of formula I in free base form is reacted with a base affordinga pharmaceutically acceptable cation, using a conventional procedurewell known in the art.

Further, when an optically active form of a compound of formula I isrequired, a racemic form of the said compound may be reacted with anoptically-active form of a suitable organic base, for example brucine,coniine, 2-pipecoline or an N,N,N-trialkyl(1-phenylethyl)ammoniumhydroxide such as N,N,N-trimethyl-(1-phenylethyl)ammonium hydroxidefollowed by conventional separation of the diastereoisomeric mixture ofsalts or complexes thus obtained, for example by fractionalcrystallisation from a suitable solvent, for example a (1-4C)alkanol,whereafter the optically-active form of the said compound may beliberated by treatment with acid using a conventional procedure, forexample using an aqueous mineral acid, such as dilute hydrochloric acid.

The property of inhibiting the enzyme aldose reductase may bedemonstrated in the following standard laboratory test. Thus, rats aremade diabetic (as evidenced by severe glucosuria being present) bydosing with streptozotocin. The animals are then dosed daily with thetest compound for 5 days. The animals are then killed and the eye lensesand sciatic nerves are removed. After a standard work-up procedure theresidual sorbitol levels in each tissue are determined by gas liquidchromatography after conversion to the poly-trimethylsilyl derivatives.Inhibition of aldose reductase in vivo is then assessed by comparing theresidual sorbitol levels in tissues from the dosed diabetic group ofrats with those of an undosed group of diabetic rats and an undosed,normal group of rats.

Alternatively, a modified test may be used in which the streptozotocininduced diabetic rats are dosed daily with test compound for two days.After 2-4 hours from the final dose the animals are killed and thesciatic nerves are removed and assessed for residual sorbitol levels asdescribed above.

In general the compounds of formula I produce significant inhibition ofthe enzyme aldose reductase (as measured by the effects on residualsorbitol levels) in either of the above tests at an oral dose of 100mg./kg. or much less without any signs of overt toxicity or otheruntoward effects at the active dose or several multiples thereof. By wayof illustration, the novel compound1'-(3,4-dichlorobenzyl)spiro[pyrrolidine-3,3'-indoline]-2,2',5-trioneproduced a residual sorbitol level in the sciatic nerve which isapproximately 20% of that obtained in control, undosed diabetic rats,following oral dosing at 50 mg./kg. for 2 days.

However, preferred compounds of formula I, such as those definedhereinbefore, in general reduce the residual sorbitol level in thesciatic nerve to that in normal undosed rats when administered at anoral dose in the range 5 to 30 mg./kg.

The property of inhibiting the enzyme aldose reductase may also bedemonstrated in vitro. Thus, purified aldose reductase is isolated inknown manner from bovine lenses. The percentage inhibition of thisenzyme's ability in vitro to reduce aldoses to polyhydric alcohols, andparticularly to reduce glucose to sorbitol, caused by a test compound isthen determined using standard spectrophotometric methods. In this testthe compounds of formula I in general show significant inhibition of theenzyme aldose reductase at a concentration of about 10⁻⁶ M or much less.Compounds of formula I possessing potent inhibitory properties in thisin vitro test and yet not particularly active by oral administration inthe above in vivo tests may nevertheless be applied in an in vivotherapeutic or prophylactic situation, for example by topicaladministration direct to the tissue or organ in which inhibition of theenzyme is required, for example by topical administration to the eye.

However, the compounds of formula I will primarily be administeredsystemically (preferably by mouth) to a warm-blooded animal to producean inhibitory effect on the enzyme aldose reductase, for example at adaily dose of 0.5 to 25 mg./kg. In man it is envisaged that a totaldaily dose in the range 10 to 750 mg. per man will be administered, ifnecessary, given in divided doses.

Topical formulations may be administered to the eye of an animal, forexample man or dogs, requiring treatment for diabetic cataracts orretinopathy in a conventional manner, for example using a drop oreyewash topical formulation.

The invention also provides a method for inhibiting aldose reductase ina warm-blooded animal requiring such treatment which method comprisesadministering to said animal an aldose reductase inhibitory amount of acompound of formula I as defined anywhere hereinbefore, or apharmaceutically acceptable salt thereof.

The compositions of the invention may also contain one or more otheragents which may or are known to have a useful effect in the treatmentof diabetes or galactosemia, for example a hypoglycaemic agent astolbutamide, chlorpropamide, or glybenclamide.

The invention will now be illustrated by the following non-limitingExamples in which, unless otherwise stated:

(i) all evaporations were carried out by rotary evaporation in vacuo:

(ii) all operations were carried out at room temperature, that is in therange 18°-26° C.;

(iii) petroleum ether (b.p. 60°-80° C) is referred to as "petrol 60-80",and other petroleum ether fractions accordingly;

(iv) yields (where given) are for illustration only and are notnecessarily the maximum attainable from the process in question;

(v) chromatography was carried out on silica gel (Art. No. 7734,available from E Merck, Darmstadt, West Germany) using conventionalprocedures; and

(vi) all the final products of formula I were of satisfactory purity asindicated by TLC, NMR spectroscopy mass spectroscopy and/ormicroanalysis:

EXAMPLE 1 (All parts by weight)

A mixture of1'-(4-chlorobenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2'5-trione (50parts), lactose (27 parts) and maize starch (20 parts), was stirredthoroughly and a paste formed from maize starch (2 parts) and water (40parts) was added and thoroughly mixed in. The resultant mass was passedthrough a 16 mesh screen, then dried at 60° C. and passed through a 20mesh screen. Magnesium stearate (1 part) was added to the granulesobtained, and the whole compressed by conventional means into tablets,containing 10, 20, 50 and 100 mg. of active ingredient and suitable fororal administration for therapeutic purposes.

Using a similar procedure, but replacing the active ingredient by anyother compound of formula I or a salt thereof, for example a knowncompound as described hereinbefore or a novel compound as describedhereinafter, tablets containing 10, 20, 50 and 100 mg. of activeingredient may be obtained.

EXAMPLE 2 (All parts by weight)

A mixture of1'-(4-chlorobenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione (50parts), calcium carbonate (20 parts) and polyethyleneglycol (averagemolecular weight 4000) (30 parts) was vigorously stirred to obtain auniform powdered form. This material was then charged into gelatinecapsules using a conventional procedure such that each capsule contains10, 20, 50 or 100 mg. of active ingredient suitable for oraladministration for therapeutic purposes.

The active ingredient in the above procedure may be replaced by anyother compound of formula I or a salt thereof mentioned herein.

EXAMPLE 3

A mixture of1'-(3,4-dichlorobenzyl)-4-ethoxycarbonyl-spiro[pyrrolidine-3,3'-indoline]-2,2'5-trione(8.2g.) and acetic acid (50 ml.) was heated under reflux for 22 hours. Thesolution obtained was cooled and poured into water (300 ml.). The solidwhich formed was collected by filtration and recrystallised frommethanol to give1'-(3,4-dichlorobenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2'5-trione(2.3 g.), m.p. 203°-204° C.

The starting material was obtained as follows:

A mixture of 1-(3,4-dichlorobenzyl)-indoline-2,3-dione (8.0 g.), ethylcyanoacetate (2.95 g.) and piperidine (0.2 ml.) in ethanol (100 ml.) washeated under reflux for 4 hours. The mixture was then allowed to coolfor 16 hours. The solid which had formed was collected by filtration andwashed with methanol to give ethyl2-[1-(3,4-dichlorobenzyl)-2-oxo-3-indolinidyl]-2-cyanoacetate (A) (6.5g.), m.p. 140°-143° C.

Potassium cyanide (1.1 g.) was added to a solution of A (6.5 g.) indimethyl sulphoxide (50 ml.) The mixture was stirred for 5 hours,diluted with water (60 ml.) and acidified to pH 5 with 2M hydrochloricacid. The resultant mixture was extracted with ether (3×100 ml.). Thecombined extracts were washed with water (2×50 ml.), dried (MgSO₄) andevaporated. The brown oil (containing ethyl2-[1-(3,4-dichlorobenzyl)-3-cyano-2-oxo-3-indolinyl]-2-cyanoacetate)(7.3 g.) obtained was dissolved in methanol (100 ml.) and the resultantsolution was saturated with hydrogen chloride gas at 0°-5° C., then leftat ambient temperature for 2 days and finally heated under reflux for 4hours. The solution was cooled and a small quantity of solid was removedby filtration. The filtrate was diluted with water (200 ml.) and thesolid which formed was collected by filtration to give1'-(3,4-dichlorobenzyl)-4-ethoxycarbonyl-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione(6.0 g.), m.p. 60°-85° C.

EXAMPLES 4 and 5

Using a similar procedure to that described in Example 3, there wereobtained:

(Example 4):1'-(4-methylbenzyl)-spiro[pyrrolidine3,3'-indoline]-2,2',5-trione, m.p.218°-220° C. (EtOAc/petrol 60-80) in 94% yield, starting from4-methoxycarbonyl-1'-(4-methylbenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione(B); and

(Example 5):1'-(4-bromo-2-fluorobenzyl)-7'-methylspiro[pyrrolidine-3,3'-indoline]2,2',5-trione,m.p. 210°-211° C. (EtOAc/petrol 60-80) in 43% yield starting from1'-(4-bromo-2-fluorobenzyl)-4-ethoxycarbonyl-7'-methyl-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione(C).

The initially formed intermediatespiro[pyrrolidine-3,3'-indoline]-2,2',5-trione-4-carboxylic acid offormula II was decarboxylated during the reaction.

The starting materials were obtained in a similar manner to A in Example3:

B, was obtained as a solid, m.p. 160°-162° C. (EtOAc/petrol 60-80) andwas itself obtained from ethyl2-[3-cyano-7-methyl-1-(4-methylbenzyl)-2-oxo-3-indolinyl]-2-cyanoacetate,m.p. 128°-130° C. (EtoAc/petrol 60-80); in turn obtained by addition ofcyanide to ethyl2-[1-(4-methylbenzyl)-2-oxo-3-indolinidyl]-2-cyanoacetate, m.p. 143-145;itself formed by reaction of ethyl cyanoacetate with1-(4-methylbenzyl)indoline-2,3-dione.

C, was obtained as a solid of satisfactory purity by TLC (SiO₂:EtOAc/petrol 60-80) and was itself obtained from ethyl2-[1-(4-bromo-2-fluorobenzyl)-3-cyano-7-methyl-2-oxo-3-indolinyl]-2-cyanoacetate, m.p. 130°-132° C. (EtOH); in turnobtained by addition of cyanide to ethyl2-[1-(4-bromo-2-fluorobenzyl)-7-methyl-2-oxo-3-indolinidyl]-2-cyanoacetate,m.p. 159°-160° C.; itself formed by reaction of ethyl cyanoacetate with1-(4-bromo-2-fluorobenzyl)-7-methylindoline-2,3-dione.

EXAMPLE 6

1'-(4-bromo-2-fluorobenzyl)-4-cyano-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione(1.0 g.) was heated under reflux in 48% w/w hydrogen bromide in aceticacid (30 ml.) for 90 minutes. The solution was poured into water (120ml.). The precipitate was collected, washed with water (100 ml.), airdried and recrystallised twice from 2-propanol to give1'-(4-bromo-2-fluorobenzyl)spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione(0.25 g.), m.p. 218°-220° C.

The starting material was obtained as follows:

Potassium cyanide (5.85 g.) was added to a solution of ethyl2-[1-(4-bromo 2-fluorobenzyl)-2-oxo3-indolinidyl]-2-cyanoacetate (D)(35.0 g.) in methanol (80 ml.). The mixture was stirred for 2 hours,cooled to 0° C. and then saturated with dry hydrogen chloride at 0°-1O°C. The solution obtained was left overnight at ambient temperature,heated at 50°-55° C. for 1 hour and then under reflux for 4 hours. Thecooled reaction solution deposited a solid which was collected; washedwith water, air dried and then heated under reflux in acetic acid (85ml.) for 12 hours. This mixture was cooled and the solid residue removedby filtration. The filtrate was evaporated, residual acetic acid beingremoved by azeotropic evaporation with toluene (3×150 ml.). The oilyresidue obtained was dissolved in ethyl acetate (100 ml.) and absorbedonto chromatographic silica gel (30 g.) by evaporation of the solvent.The residue was added to a column of silica gel (300 g.) made up intoluene. Elution with an increasing concentration of ethyl acetate intoluene (up to 25% v/v) and combination and evaporation of thosefractions containing the major component (relative flow value 0.6), gave1'-(4-bromo-2-flurobenzyl)-4-cyano-spiro[pyrrolidine3,3'-indoline]-2,2',5-trione(5.5 g.), m.p. 208°-210° C., after recrystallisation from ethylacetate/petrol 60-80.

The starting material (D) was obtained as a red solid, m.p. 144°-147° C.by reaction of ethyl cyanoacetate with1-(4-bromo-2-fluorobenzyl)indoline-2,3-dione, using a similar procedureto that described for the corresponding starting material for A inExample 3.

EXAMPLE 7

Sulphuryl chloride (2.74 g.) was added to a stirred suspension of1'-(3,4-dichlorobenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione(3.0 g.) in acetic acid (50 ml.). The mixture was stirred at 60° C. for5 hours, cooled to ambient temperature and then stirred at thistemperature for 16 hours. The mixture was then poured into water (250ml.). The white solid which formed was collected by filtration, washedwith water, air dried and recrystallised from 2-propanol to give5'-chloro-1'-(3,4-dichlorobenzyl)spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione(1.9 g.), m.p. 268°-270° C.

EXAMPLE 8

Sodium hydride (0.192 g., 50% w/w oil dispersion) was added to a stirredsolution of1'-(3,4-dichlorobenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione(1.5 g.) in dry N,N-dimethylformamide (DMF) (20 ml.) under a nitrogenatmosphere. The solution was stirred for 30 minutes and thenchloromethyl pivaloate (0.60 g.) was added. The mixture was stirred for20 hours and then poured into water (30 ml.) The mixture obtained wasextracted with ethyl acetate (2×40 ml.). The combined extracts werewashed with water (2×15 ml.) dried (MgSO₄) and evaporated. The residuewas dissolved in ethyl acetate (20 ml.). Chromatographic silica gel (10g.) was added to the solution and then the solvent was evaporated. Theresidue was added to a column of silica gel (400 g.) made up in ethylacetate/petrol (60-80 (1:1 v/v). This solvent mixture was used to elutethe column. Evaporation of those combined fractions of eluate containingthe major component [relative flow value 0.6, as judged by TLC (SiO₂ :50% v/v EtOAc/toluene)]gave1'-(3,4-dichlorobenzyl)-3-pivaloyloxymethyl-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trioneas an oil which solidified slowly to give a solid (0.55 g.), m.p.134°-135° C. (cyclohexane).

EXAMPLE 9

A solution of ethyl2-[1-(3,4-dichlorobenzyl)-3-cyano-5-fluoro-2-oxo-3-indolinyl]-2-cyanoacetate(E) (2.0 g.) in 48% w/v hydrogen bromide in acetic acid (25 ml.) washeated under reflux for 3 hours. The solution was evaporated to halfvolume and poured into water (20 ml.). The mixture was extracted withethyl acetate (2×50 ml.). The combined extracts were washed with water(2×50 ml.), brine (50 ml.), dried (MgSO₄) and evaporated. The residualsolid was recrystallised from 2-propanol/petrol 60-80 to give1'-(3,4-dichlorobenzyl)-5'-fluoro-spiro[pyrrolidine3,3'-indoline]-2,2',5-trione (0.49 g.), m.p. 253°-254° C.

The starting material (E) was obtained as a solid, m.p. 134°-137° C.,from ethyl2-[1-(3,4-dichlorobenzyl)-5-fluoro-2-oxo-3-indolinidyl]-2-cyanoacetate(F) using an analogous procedure to that described in Example 3 for theequivalent starting material for A. The starting material (F) wassimilarly obtained as a solid, m.p. 144°-146° C. by reaction of ethylcyanoacetate with 1-(3.4-dichlorobenzyl)-5-fluoroindoline-2,3-dione,using the procedure described for the equivalent starting material inExample 3.

EXAMPLE 10

Sodium hydride (1.1 g.; 23 mM; 50% w/w oil dispersion) was added to astirred solution of spiro [pyrrolidine-3,3'-indoline]-2,2',5-trione (2.1g.; 9.7 mM) in DMF (40 ml.), under an atmosphere of nitrogen. Themixture was stirred until effervescence had ceased and then heated toapproximately 90° C. 3,4-Dichlorobenzyl chloride (2.2 g., 11.2 mM) wasadded dropwise. The reaction mixture was then allowed to cool to ambienttemperature, stirred for 16 hours, and poured into water. The aqueousmixture was acidified (concentrated hydrochloric acid) and extractedwith ethyl acetate (2×150 ml.). The combined extracts were washed withwater (3×150 ml.), brine (150 ml.), dried MgSO₄) and evaporated. Theresidual oil was purified by chromatography on silica gel (150 g.) usingan increasing gradient of ethyl acetate in toluene as eluant. Fractionswere monitored by TLC (SiO₂ : 50% v/v EtOAc/toluene) and thosecontaining the major component (relative flow value : 0.5) wereevaporated to give1'-(3,4-dichlorobenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione(0.6 g , m.p. 205°-207° C. (recrystallised twice from MeOH).

EXAMPLE 11

Ethanolic potassium hydroxide (12 ml., 1M) was added to a stirredsolution of spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione (1.0 g.) indimethyl sulphoxide (10 ml.). 4-Bromobenzyl bromide (1.4 g.) was thenadded to the clear solution which was stirred for 4 hours. This solutionwas then added to water (100 ml.). The mixture was acidified(concentrated hydrochloric acid). The precipitate was collected, washedwith water, air-dried and recrystallised from ethyl acetate/petrol 60-80to give 1'-(4-bromobenzyl)spiro[pyrrolidine-3,3-indoline]-2,2',5-trione(0.15 g.) m.p. 218°-220° C.

EXAMPLES 12-21

Using a similar procedure to that described in Example 11, the followingcompounds of formula I were obtained in yields of 10-45% starting fromthe appropriate spiro[pyrrolidine-3,3'-indoline]-2,2',5trione of formulaX (M=H) and alkylating agent of the formula Ra.Br:

    ______________________________________                                               Substituent                                                                   on benzene           m.p.   recrystallisation                          Example                                                                              ring A    Ra         (°C.)                                                                         Solvent(s)                                 ______________________________________                                        12     --        2-fluoro-4-                                                                              228-230                                                                              i-Pr.OH                                                     iodobenzyl                                                   13     --        4-chloro-2-                                                                              203-205                                                                              EtOAc/                                                      fluorobenzyl      petrol 60-80                               14     --        hexyl      110-112                                                                              EtOAc/                                                                        petrol 60-80                               15     --        cinnamyl   188-190                                                                              EtOAc/                                                                        petrol 60-80                               16     --        2-naphthyl-                                                                              212-213                                                                              EtOAc/                                                      methyl            petrol 60-80                               17     7'-fluoro 2-fluoro-4-                                                                              241-243                                                                              EtOAc/                                                      iodobenzyl        petrol 60-80                               18     --        4-bromo-2- 218-220                                                                              EtOAc/                                                      fluorobenzyl      petrol 60-80                               19     5'-chloro 4-bromo-2- 222-224                                                                              EtOAc/                                                      fluorobenzyl      petrol 60-80                               20     --        butyl      173-174                                                                              MeOH                                       21     --        3-trifluoro-                                                                             131-133                                                                              EtOAc/                                                      methylbenzyl      petrol 60-80                               ______________________________________                                         Notes                                                                         1. Aqueous potassium hydroxide was used as base in Ex. 12.                    2. In general 2.0-2.5 molecular equivalents of base and 1.0-1.2 molecular     equivalents of Ra.Br per molecular equivalent of X (M = H) were used.         3. The compounds in Examples 14-17, 19 and 21 were purified by                chromatography using a similar procedure to that described in Example 10.

7'-Fluoro-spiro[pyrrolidine-3,3'-indoline]-2,2'-5-trione was obtained asa solid (m.p. 254°-256° C.) by cyclisation of ethyl2-(3-cyano-7-fluoro-2-oxo-3-indolinyl)-2-cyanoacetate using hydogenbromide in acetic acid as described in Example 9. The cyanoacetate wasitself obtained as a brown oil from ethyl2-(7-fluoro-2-oxo-3-indolinidyl)-2-cyanoacetate, itself obtained as asolid (m. p. 165°-166° C.) from 7-fluoroisatin and ethyl cyanoacetate,using the procedures described in Example 9. 7-Fluoroisatin was obtainedas a solid (m.p. 190°-192° C.) by a conventional isatin synthesisstarting from 2-fluoroaniline.

5'-Chloro-spiro[pyrrolidine-3,3'-indoline]-2,2', 5-trione was obtainedas a solid (m.p. 295°-299° C.) by chlorination of the knownspiro[pyrrolidine-3,3'-indoline]-2,2',5-trione [Arch. der Pharmazie,(Weinheim), 1970 303, 183-191]using sulphuryl chloride and an analogousprocedure to that described in Example 7.

EXAMPLE 22

Using a similar procedure to that described in Example 11, but usingsodium ethoxide as the base, ethanol as the solvent and2,4-dichlorobenzyl chloride as the alkylating agent, there was obtained1'-(2,4-dichlorobenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2', 5-trione,m.p. 231°-233° C. (EtOAc/petrol 60-80) in 20% yield.

EXAMPLES 23-42

Using a similar procedure to that described in Example 9, but using theappropriate ethyl2-(1-substituted-3-cyano-2-oxo-3-indolinyl)-2-cyanoacetate of theformula IV (X═Y═CN, Z═CO₂ Et), the following compounds of formula I wereobtained:

    ______________________________________                                                             Substituent on                                           Example                                                                              Ra            benzene ring A                                                                              m.p. (°C.)                          ______________________________________                                        23     hexyl         7'-methyl      96-98                                     24     heptyl        7'-methyl      85-86                                     25     3-trifluoromethyl-                                                                          7'-methyl     226-228                                           benzyl                                                                 26     3-trifluoromethyl-                                                                          7'-fluoro     196-198                                           benzyl                                                                 27     hexyl         7'-fluoro      96-97                                     28     heptyl        7'-fluoro      72-73                                     29     heptyl        7'-trifluoromethyl                                                                          oil (Note 2)                               30     4-methylbenzyl                                                                              7'-trifluoromethyl                                                                          253-254                                    31     pentyl        7'-trifluoromethyl                                                                          oil (Note 3)                               32     hexyl         5'-fluoro     114-115                                    33     heptyl        5'-fluoro     105-106                                    34     4-methylbenzyl                                                                              5'-fluoro     134-135                                    35     3-trifluoromethyl-                                                                          5'-fluoro     173-174                                           benzyl                                                                 36     pentyl        7'-fluoro     118-119                                    37     3-trifluoromethyl-                                                                          7'-chloro     216-217                                           benzyl                                                                 38     4-trifluoromethyl-                                                                          7'-chloro     208-209                                           benzyl                                                                 39     4-methylbenzyl                                                                              7'-chloro     212-213                                    40     4-bromo-2-fluoro-                                                                           7'-fluoro     240-242                                           benzyl                                                                 41     3,4-dichloro- 7'-fluoro     188-190                                           benzyl                                                                 42     3,4-dichloro- 6'-chloro     191-193                                           benzyl                                                                 ______________________________________                                         Notes                                                                         1. All the products were purified by column chromatography (medium            pressure) on silica using a mixture of 10-25% v/v ethyl acetate in petrol     60-80 as eluant, and were then recrystallised (except Ex. 29 and 31) from     ethyl acetate/petrol 60-80, and obtained in yields of 10-60%                  2. NMR (90 MH.sub.z CDCl.sub.3); δ 0.85 (3H, t, CH.sub.2 CH.sub.3);     1.1-1.8 [10H, complex, (CH.sub.2).sub.5 ]; 3.1 (2H, quartet, COCH.sub.2       N); 3.9 (2H, t, NCH.sub.2); 6.9-7.7 (3H, complex, aromatic H); 9.5-10         (broad s, NH).                                                                3. NMR (90 MH.sub.z, CDCl.sub.3): δ 0.85 (3H, t, CH.sub.2 CH.sub.3)     1.1-1.8 [6H, complex, (CH.sub.2).sub.3 ]; 3.1 (2H, quartet, COCH.sub.2 N)     3.9 (2H, t, NCH.sub.2); 6.9-7.7 (3H, complex, aromatic H); 8.0-9.2 (broad     s, NH).                                                                  

The necessary starting materials of formula IV were obtained asdescribed in Example 9 and used without purification, starting from thecorresponding dark red ethyl2-(1-substituted-2-oxo-3-indolinidyl)-2-cyanoacetates of formula V(Y═CN, Z═CO₀₂ Et) (shown in the following Table), which were themselvesobtained as mixtures of geometric isomers in yields of 30-90%, using theprocedure described in Examples 9 and 3:

    ______________________________________                                        Compound             Substituent on                                           No.     Ra           benzene ring A                                                                             m.p. (°C.)                           ______________________________________                                        1       hexyl        7-methyl     56-58                                                                         (EtOH)                                      2       heptyl       7-methyl     oil*                                        3       3-trifluoromethyl-                                                                         7-methyl     oil*                                                benzyl                                                                4       3-trifluoromethyl-                                                                         7-fluoro     oil*                                                benzyl                                                                5       hexyl        7-fluoro     oil*                                        6       heptyl       7-fluoro     oil*                                        7       heptyl       7-trifluoromethyl                                                                          oil*                                        8       4-methylbenzyl                                                                             7-trifluoromethyl                                                                          oil*                                        9       pentyl       7-trifluoromethyl                                                                          gum*                                        10      hexyl        5-fluoro     106-107                                                                       (EtOAc/                                                                       petrol 60-80)                               11      heptyl       5-fluoro     78-79                                                                         (EtoH)                                      12      4-methylbenzyl                                                                             5-fluoro     192-194                                                                       (EtOH)                                      13      3-trifluoromethyl-                                                                         5-fluoro     134-135                                             benzyl                    (EtOAc/                                                                       petrol 60-80)                               14      pentyl       7-fluoro     oil*                                        15      3-trifluoromethyl-                                                                         7-chloro     131-133                                             benzyl                    (EtOH)                                      16      3-trifluoromethyl-                                                                         7-chloro     oil*                                                benzyl                                                                17      4-methylbenzyl                                                                             7-chloro     oil*                                        18      4-bromo-2-fluoro-                                                                          7-fluoro     128-130                                             benzyl                    (EtOH/Et.sub.2 O)                           19      3,4-dichlorobenzyl                                                                         7-fluoro     138-140                                                                       (EtOH/Et.sub.2 O)                           20      3,4-dichlorobenzyl                                                                         6-chloro     159-162                                                                       (EtOH/Et.sub.2 O)                           ______________________________________                                         *Note: essentially pure by TLC (SiO.sub.2 : 25% EtOAC/petrol 60-80)           showing `E` and `Z` geometric isomers as separate red spots.             

The 1-substituted-indoline-2,3-diones of formula VI, used for the aboveand earlier Examples, were prepared by the following procedure, which issimilar to that described by Schaefer [Archiv.Pharmazie (Weinheim),1970, 303, 183-191]:

A solution of indoline-2,3-dione in DMF (10 ml. per gram ofindoline-2,3-dione) was stirred with anhydrous potassium carbonate (1.5molecular equivalents) for 20-30 minutes. The appropriate alkyl bromideor benzyl chloride or bromide (1.1 molecular equivalents) was then addedand the mixture heated at 80°-85° C. for 1-2 hours, and then poured intoan excess of ice-water (approximately 10x volume of DMF). The resultantorange solid was separated and air-dried to give the appropriate1-substituted-indoline-2,3-dione.

Using this procedure, the following compounds of formula VI wereobtained:

    ______________________________________                                                             Substituent                                                                   on benzene   m.p.                                        Compound                                                                              Ra           ring A       (°C.)                                ______________________________________                                        a       hexyl        7-methyl     46-48                                       b       heptyl       7-methyl     55-56                                        c*     3-trifluoromethyl-                                                                         7-methyl     169-171                                             benzyl                                                                 d*     3-trifluoromethyl-                                                                         7-fluoro     108-109                                             benzyl                    (iPrOH)                                     e       hexyl        7-fluoro     99-100                                      f       heptyl       7-fluoro     84-85                                       g       heptyl       7-trifluoromethyl                                                                          43-44                                       h       4-methylbenzyl                                                                             7-trifluoromethyl                                        i       pentyl       7-trifluoromethyl                                                                          61-63                                       j       hexyl        5-fluoro     53-54                                                                         (petrol 60-80)                              k       heptyl       5-fluoro     67-68                                       l       4-methylbenzyl                                                                             5-fluoro     130-132                                      m*     3-trifluoromethyl-                                                                         5-fluoro     145-146                                             benzyl                    (iPrOH)                                     n       pentyl       7-fluoro     82-83                                        o*     3-trifluoromethyl-                                                                         7-chloro                                                         benzyl                                                                 p*     4-trifluoromethyl-                                                                         7-chloro     160-161                                             benzyl                                                                q       4-methylbenzyl                                                                             7-chloro     185-187                                     r       4-bromo-2-fluoro-                                                                          7-fluoro     159-161                                             benzyl                    (EtOAc/                                                                       petrol 60-80)                               s       3,4-dichlorobenzyl                                                                         7-fluoro     147-148                                                                       (EtOAc/                                                                       petrol 60-80)                                t*     3,4-dichlorobenzyl                                                                         6-chloro     180-182                                                                       (i-PrOH)                                     u*     3,4-dichlorobenzyl                                                                         none         183-184                                                                       (EtOAc/                                                                       petrol 60-80)                                v*     4-methylbenzyl                                                                             none         141-143                                                                       (EtOAc/                                                                       petrol 60-80)                               w       4-bromo-2-fluoro-                                                                          7-methyl     154-156                                             benzyl                                                                 x*     3,4-dichlorobenzyl                                                                         5-fluoro     190-192                                                                       (EtOAc/                                                                       petrol 60-80)                               y       4-bromo-2-fluoro-                                                                          none         151-153                                             benzyl                    (i-PrOH/                                                                      petrol 60-80)                               ______________________________________                                         Note*:                                                                        These compounds were obtained using the appropriate benzyl chloride. The      remaining compounds were obtained using the appropriate alkyl bromide or      benzyl bromide.                                                          

EXAMPLE 43

1'-(3,4-Dichlorobenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trione(1.87 g.) was dissolved in water (50 ml.) containing sodium hydroxide(0.20 g.). Any residual solid was removed by filtration. The filtratewas evaporated, remaining traces of water being removed by azeotropicdistillation with toluene. The residue was dried in vacuo (over P₄ O₁₀).There was thus obtained the sodium salt of1'-(3,4-dichlorobenzyl)-spiro[pyrrolidine-3,3'-indoline]-2,2',5-trioneas an amorphous solid having a satisfactory microanalysis.

EXAMPLE 44 (All parts by weight)

An aqueous solution containing the sodium salt of1'-(4-bromo-2-fluorobenzyl)-7'-methyl-spiro[pyrrolidine-3,3'-indoline-2,2',5-trione(10 parts), sodium bisulphite (as antoxidant, 3 parts) and phenylmercuric acetate (as preservative, 0.02 parts) in water (1000 parts) wasacidified with sufficient hydrochloric acid to bring the pH into therange 7.0-7.6. The solution was then sterile filtered in conventionalmanner in order to remove particulate contaminants. There is thusobtained a sterile solution containing approximately 1% of the activeingredient suitable for topical administration, for example to the eye,for medicinal purposes.

The active ingredient may be replaced by another compound of formula Ior a salt thereof as described herein.

An ophthalmically acceptable buffer system, for example sodiumborate/boric acid, may be included in the solution if desired.

Example 45

Using a similar procedure to that described in Example 1 or 2, butreplacing the active ingredient by a biodegradable precursor of acompound of formula I as described herein, there may be made furthercompositions according to the invention suitable for oral administrationfor therapeutic purposes.

What is claimed is:
 1. A pharmaceutical composition for inhibiting theenzyme aldose reductase comprising as active ingredient an effectiveamount of a 1'-substituted-spiro(pyrrolidine3,3'-indoline)-2,2',5-trioneof the formula: ##STR15## wherein Ra is benzyl bearing two independentlyselected halogeno substituents located at positions 2 and 4, or 3 and 4,or is benzyl bearing a bromo or trifluoromethyl substituent located atposition 3 or 4; and benzene ring A is unsubstituted or bears one or twosubstituents independently selected from halogeno, (1-4C)alkyl,trifluoromethyl and nitro; or a salt thereof with a base affording apharmaceutically acceptable cation; or the non-toxic, biodegradable1-pivaloyloxymethyl precursor thereof; together with a pharmaceuticallyacceptable diluent or carrier.
 2. A composition as claimed in claim 1wherein, in the active ingredient, the halogeno substituents present aspart of Ra are independently selected from fluoro, chloro, bromo or iodosubstituents and the substituents which may be present on the benzenering A are independently selected from fluoro, chloro, bromo, iodo,methyl, ethyl, trifluoromethyl and nitro substituents located at the 5',6' or 7'-position.
 3. A composition as claimed in claim 1 wherein, inthe active ingredient, Ra is 3,4-dichlorobenzyl, 2-fluoro-4-iodobenzylor 4-bromo-2-fluorobenzyl; and benzene ring A is unsubstituted or bearsa fluoro, chloro, bromo methyl or trifluoromethyl substituent located inthe 5', 6' or 7'-position.
 4. A composition as claimed in claim 1 whichis in a form suitable for oral, parenteral, rectal or topical opthalmicadministration.
 5. A composition for oral administration as claimed inclaim 4 which is in the form of a tablet, capsule, granule, dispersiblepowder, syrup, elixir, emulsion, suspension or gel.
 6. A composition fortopical ophthalmic administration as claimed in claim 4 which is in theform of an ointment, gel or sterile solution.
 7. A method of inhibitingthe enzyme aldose reductase in a warm-blooded animal requiring suchtreatment which comprises administering to said animal an aldosereductase inhibitory amount of a compound of formula I, according toclaim 1, or a salt thereof with a base affording a pharmaceuticallyacceptable cation, or the non-toxic, biodegradable 1-pivaloyloxymethylprecursor thereof.
 8. A composition according to claim 1 wherein theactive ingredient is a compound selected from compounds where Ra and thebenzene ring A are as follows:

    ______________________________________                                        Ra                Benzene ring A substituent                                  ______________________________________                                        3,4-dichlorobenzyl                                                                              unsubstituted                                               2-fluoro-4-iodobenzyl                                                                           unsubstituted                                               4-bromo-2-fluorobenzyl                                                                          unsubstituted                                               4-bromo-2-fluorobenzyl                                                                          5'-chloro                                                   3,4-dichlorobenzyl                                                                              5'-chloro                                                   3,4-dichlorobenzyl                                                                              5'-fluoro                                                   3,4-dichlorobenzyl                                                                              7'-fluoro                                                   4-bromo-2-fluorobenzyl                                                                          7'-fluoro                                                   4-bromo-2-fluorobenzyl                                                                          7'-methyl                                                   2-fluoro-4-iodobenzyl                                                                           7'-fluoro                                                   ______________________________________                                    


9. A composition according to claim 8 wherein Ra is4-bromo-2-fluorobenzyl and the benzene ring A has a 7' methylsubstituent.